1. Field of the Invention
The present invention relates to a transfer belt which has a surface on which a toner image formed on the surface of an image-supporting member is transferred and once maintained prior to transferring the toner image onto a recording medium such as paper, and transfers the toner image onto the recording medium in an image-forming apparatus such as a copying machine and a printer, and also concerns an image-forming apparatus having such a transfer belt.
2. Description of the Prior Art
In an image-forming apparatus using an electrophotographic process, after an image-supporting member constituted of a photosensitive member has been uniformly charged, an electrostatic latent image is formed thereon by using a laser beam or the like, and the latent image is then developed by charged toner. Then, the toner image is primary-transferred onto a transfer member, and then secondary-transferred from the transfer member onto a recording medium. This system is known as an intermediate transfer system. With respect to the transfer member, a transfer belt having a belt shape is often used. The problem with the image-forming method of this type is that, after the transfer belt has been used for a long time, the surface of the transfer belt is contaminated by toner or additive agents to the toner to cause degradation in image quality.
Conventionally, in order to solve this problem, the following techniques have been proposed as means for suppressing toner adhesion onto the surface of a transfer belt (improvement for anti-filming property).                1. To use fluororesin as a belt-forming material (for example, Japanese Patent Application Laid-Open No. 2002-365866);        2. To use a thermoplastic resin on which a fluororesin surface layer is formed, as a belt-forming material (for example, Japanese Patent Application Laid-Open No. 10-207242);        3. To disperse fluorine fine particles on the surface of a thermoplastic resin belt (for example, see U.S. Pat. No. 5,666,193);        4. To coat the surface of a thermoplastic resin belt with a silicone resin (for example, Japanese Patent Application Laid-Open No. 4-029275).        
The use of fluororesin as a belt-forming member, however, causes a reduction in the electric resistance in the belt and the subsequent degradation in image quality upon application of power, although it improves the anti-filming property.
The use of a belt in which fluorine fine particles are dispersed or a belt on the surface of which a fluororesin layer is formed fails to sufficiently carry out the primary transferring process to cause an image loss or the like, although it provides a sufficient toner-releasing property and improves the anti-filming property. This also causes abrasion in a cleaning blade that is placed in contact with the transfer belt, resulting in failure in exerting its functions.
Another problem is that the belt coated with silicone resin tends to cause separation of the coat layer during endurance operations.